Network Working Group M. Boucadair
Internet-Draft C. Jacquenet
Intended status: Standards Track Orange
Expires: October 28, 2017 April 26, 2017
LISP Subscriptiondraft-boucadair-lisp-subscribe-05
Abstract
Mapping Services in Locator/ID Separation Protocol (LISP) networks
are key to proper LISP forwarding operation. When considering the
deployment of LISP at large scale, these Mapping Services are even
more crucial for the sake of the LISP forwarding efficiency. This
document introduces two additional LISP messages that are meant to
facilitate the dynamic discovery of Mapping Systems, improve Ingress
Tunnel Routers (ITR) recovery times and optimize the solicitation of
the LISP Mapping System as a function of the ITR location, in
particular.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 28, 2017.
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of several Mapping Services is likely to improve the overall LISP
forwarding serviceability.
1.1. Issues
This section lists a set of issues that need further investigation:
Discover ITRs: Current LISP design does not allow to automatically
discover active ITRs of a LISP domain (nor the mapping system of a
given domain is aware of ITRs of the same domain that can solicit
its services, let alone ITRs of other domains). The solution
proposed in this document allows to fill that gap.
Optimize EID-ROLC resolution time: Leaf LISP networks can be better
serviced, for example by avoiding the cascading of Map-Resolvers,
or by avoiding the solicitation of a Map-Resolver that is located
an ocean away, etc. Policies should be taken into account when
configuring Map-Resolver information on an ITR for improving EID-
to-RLOC resolution. These policies should be modified and
adjusted according to various events (e.g., installation of an
additional Map-Resolver).
Accomodate Map-Resolvers constraints: Allows for the protocol to
redirect a requesting ITR to another Map-Resolver when some events
occur, such as an overload of the initially targeted Map-Resolver
or when Map-Resolvers are optimized to service a set of
destination EIDs, etc.
Faster Recovery of mapping entries: Whenever an ITR fails for some
reason, the faulty ITR needs to recover at least the list of
mappings for the most popular prefixes in a timely manner, in
particular. Policies for mapping entries (to be recovered) are
deployment-specific.
Receive push notifications: For LISP leaf networks that would need
to maintain an up-to-date mapping table for a set of destination
EIDs (or even the global mapping table) to avoid issues such as
the loss of a first packet or to optimize LISP forwarding delay
(and therefore the overall forwarding efficiency), a dynamic push
mechanism would be helpful.
1.2. Assumptions
This document makes the following assumptions:
o Various LISP players (network operators, service providers, etc.)
are likely to deploy and operate different LISP Mapping Systems.
Multiple Mapping Systems will therefore coexist for various
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reasons, e.g., avoid country-centric governance, allow for
distinct technologies to implement the mapping service, business
opportunities, service innovation, etc.
o Interconnection between these Mapping Systems is required for the
sake of global connectivity and also to minimize the risk of
fragmenting the Internet.
o Mapping Services are supposed to be dimensioned to maintain a
global mapping database for the entire LISP-enabled Internet.
o Mapping Service providers may offer advanced services to their
customers such as maintain local caches (a la CDN), or update ITR
mapping entries that match some criteria requested by a leaf LISP
network, redirect ITR requests to the closest Map-Resolvers,
structure the mapping resolution service so that the resolution
time is optimized, etc.
o The entries of the mapping tables are exchanged between these
Mapping systems so that Map-Request messages can be processed as
close to the LISP leaf networks as possible.
o A leaf LISP-enabled network subscribes to the Mapping Service
provided by one or several Mapping Service operators.
o The contribution of each player involved in the provisioning and
the operation of a LISP-based connectivity forwarding service
should be rationalized so that clear interfaces are defined and
adequate mechanisms for troubleshooting, diagnosis and repair
purposes can be easily implemented and adopted. The inability of
identifying what is at the origin of the degradation of a LISP
connectivity service is seen as one of the hurdles that are likely
to jeopardize LISP deployments at large scale.
1.3. Improving LISP Mapping Services
This document specifies a couple of additional LISP messages that are
meant to improve the subscription to Mapping Services, let alone
their serviceability. They are described in the following sections.
A simple method to redirect ITR-originated mapping requests towards
another Map-Resolver when some conditions are met (e.g., overload of
a Map-Resolver, enforcement of traffic engineering policies, etc.) is
defined in Section 2 and Section 3.
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o B (bulk-support bit): When set, this flag indicates that the
originating ITR supports mapping bulk retrieval method (e.g.,
[I-D.boucadair-lisp-bulk]).
o I (immediate-retrieval bit): When set, this flag indicates that
the originating ITR requests immediate retrieval of the portion of
the mapping table that matches the filters included in the
request.
o Rsv: reserved bits, MUST be sent as 0 and MUST be ignored when
received.
o Filter Count: This field indicates the number of the filters
included in the message.
o Nonce, Key ID, Authentication Data Length, and Authentication Data
are similar to those of a LISP Map-Register message ([RFC6830]).
o Expiry Timer: This field indicates, in seconds, the validity timer
for the subscription.
o Length: This field indicates, in octets, the length of the filter
that is encoded in the "Filter" field.
o Filter: This field carries a destination EID (or a set thereof)
that is encoded as an UTF-8 string. This specification allows to
convey IP prefix literals, Names and/or AS numbers. One or
multiple filters may be present in a request. IPv4 prefixes are
encoded as IPv4-mapped IPv6 prefixes [RFC4291] (i.e., starting
with ::ffff:0:0/96). A mix of names, IP prefixes and AS numbers
may be enclosed in the same request. The value 0 is used to
delete existing filters. Filters MUST be applied in the order
they appear in the request.
3. Map-Subscribe-Ack Message Format
The format of the Map-Subscribe-Ack message is shown in Figure 2.
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o B (bulk-support bit): When set, this flag indicates that the Map-
Resolver supports mapping bulk retrieval method (e.g.,
[I-D.boucadair-lisp-bulk]).
o I (immediate-retrieval bit): When set, this flag indicates that
the Map-Resolver will initiate an immediate push cycle of the
portion of the mapping table that matches the filters included in
the request.
o R (Redirect bit): When set, this flag indicates that a redirect
Map-Resolver is enclosed in the message.
o Rsv: reserved bits, MUST be set to 0 and MUST be ignored when
received.
o Result: indicates the result code of the processing of the Map-
Subscribe request. The following codes are defined:
0: SUCCESS. This code is used to indicate the request is
successfully processed.
1: PARTIAL-FILTERS-INSTALLED-LIMIT. This code is used to indicate
a request is successfully processed but some filters were not
installed because the number of filters carried in the initial
Map-Subscribe message exceeds the filter limit.
2: PARTIAL-FILTERS-INSTALLED-BAD. This code is used to indicate a
request is successfully processed but some filters were not
installed because they were malformed.
3: PARTIAL-FILTERS-INSTALLED-LOCAL. This code is used to indicate
a request is successfully processed but some filters were not
installed because of local reasons. The ITR SHOULD, after a
certain timer expires, send a Map-Subscribe request message for
the set of filters that are not included in the Map-Subscribe-
Ack message received by the ITR in response to its initial Map-
Subscribe request message.
4: FILTERS-PROHIBITED. This code is used to indicate a request is
successfully processed but the installation of filters is
prohibited.
o Filter Count: This field indicates the number of the filters
included in the message.
o Nonce, Key ID, Authentication Data Length, and Authentication Data
are similar to those of a LISP Map-Register message ([RFC6830]).
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o Expiry Timer: This field indicates, in seconds, the validity timer
for the subscription.
o Length: This field indicates, in octets, the length of the filter
that is encoded in the "Filter" field.
o Filter: This field carries the set of filters that were
successfully installed.
o Redirect Map-Resolver IP Address (128 bits): When the R-bit is
set, this field carries the IP address of the Map-Resolver where
mapping requests should be redirected. An IPv4 address is encoded
as an IPv4-mapped IPv6 address.
4. Generating a Map-Subscribe Message
The A-bit of a Map-Subscribe message MUST be set to 0.
An ITR uses the U-bit to inform a Map-Resolver whether it is ready to
handle unsolicited Map-Reply messages or not. The ITR MUST set the
U-bit when it supports such capability.
An ITR uses the B-bit to inform a Map-Resolver whether it supports
the mapping bulk transfer method or not. The ITR MUST set to the
B-bit when it supports such method (e.g., [I-D.boucadair-lisp-bulk]).
An ITR that joins the LISP network is likely to delete all
notifications that are bound to its RLOCs. It does so by including a
Null filter prior to any filter that it wishes the Map-Resolver to
record. Note, an ITR can indicate a Null filter using one of these
methods:
1. Send a Map-Subscribe message with a "Filter Count" set to 0, or
2. Include a Filter with a 'Filter" field set to zeros.
An ITR that loses its mapping cache for some reason SHOULD generate a
Map-Subscribe message towards its Map-Resolver(s) with the I-bit set.
An ITR MAY generate several Map-Subscribe messages to make the Map-
Resolver install the required filters. Nevertheless, an ITR MUST
expect that the Map-Resolver may limit the number of filters that may
be installed. Filters that are not accepted or not processed by the
Map-Resolvers are not included in a Map-Subscribe-Ack message.
An ITR that wants to delete one or a set of filters MUST generate a
Map-Subscribe message which carries those filters with an Expiry
Timer set to 0.
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A Map-Resolver that does not support the Map-Subscribe message MUST
silently ignore any Map-Subscribe message it receives.
Map-Resolvers MUST support a configurable parameter to enable/disable
the processing of Map-Subscribe messages. The default value is set
to "enabled".
A Map-Resolver SHOULD support a configuration parameter to limit the
number of filters per leaf LISP network, per ITR, etc.
If a Map-Resolver receives a Map-Subscribe message and is enabled to
process it, a Map-Resolver MUST reply with a Map-Subscribe-Ack
message to acknowledge the receipt of the corresponding Map-Subscribe
message.
When building a Map-Subscribe-Ack message, the Map-Resolver MUST:
o Set the A-bit to indicate this is a response to a Map-Subscribe
request.
o Set the U-bit if it supports the unsolicited Map-Reply capability,
except if a redirect Map-Resolver is to be returned.
o Set the B-bit if it supports a method for mapping bulk transfer,
except if a redirect Map-Resolver is to be returned.
o Set the R-bit if it wants to inform the requesting ITR about
another Map-Resolver it should contact. The Map-Resolver MAY
return a set of filters that are to be applied by the ITR to
select the Map-Resolver (i.e., destination EID Map-Resolver
address selection).
o Echo the I-bit if the Map-Resolver accepts to initiate unsolicited
mapping retrievals, except if a redirect Map-Resolver is to be
returned.
o If no redirect is enabled and the request includes one or several
filters, the Map-Resolver MUST echo the filters it succeeds to
install, and in the same order of appearance, in the Map-
Subscribe-Ack message.
o If the Map-Resolver is configured with maximum and minimum values
for the expiry timer, the Map-Resolver MUST adjust the Expiry
Timer enclosed in the request so that it does not exceed these
boundary values.
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If the I-bit is set in the Map-Subscribe request and the Map-Resolver
supports the unsolicited mapping retrieval capability, the Map-
Resolver SHOULD generate unsolicited Map-Reply messages or dedicated
bulk transfer messages that carry the EID-RLOC mapping entries that
match the filters already present in the Mapping System for that ITR
or that match those carried by the Map-Subscribe message.
If filters are included in the request, the Map-Resolver MUST extract
those filters and update its mapping system subscription for that ITR
accordingly. In particular, the Map-Resolver MUST delete all filters
that are active for that ITR if a Null filter is included in the Map-
Subscribe request or if the expiry timer is null.
If filters are not allowed for a given ITR, the 'Result' field MUST
be set to FILTERS-PROHIBITED.
If all filters are successfully installed, the 'Result' field MUST be
set to SUCCESS.
If the Map-Resolver fails to install some of the filters included in
a request because the filter limits for that ITR are exceeded, it
MUST NOT echo the corresponding filters in the Map-Subscribe-Ack
message. The 'Result' field MUST be set to PARTIAL-FILTERS-
INSTALLED-LIMIT.
If the Map-Resolver fails to install some of the filters included in
a request because these filters were malformed, it MUST NOT echo the
corresponding filters in the Map-Subscribe-Ack message; only
successfully installed filters MUST be included. The 'Result' field
MUST be set to PARTIAL-FILTERS-INSTALLED-BAD.
If, for some other reasons, the Map-Resolver fails to apply the
filters included in a request, it MUST NOT echo the said filters in
the Map-Subscribe-Ack message; only the successfully installed
filters MUST be included. The 'Result' field MUST be set to PARTIAL-
FILTERS-INSTALLED-LOCAL.
If a filter that is included in the request is more specific than a
filter that is already present in the mapping system for the same
ITR, the Map-Resolver MUST NOT add a new filter but MUST include the
old filter in the response to the requesting ITR.
If a more specific filter exists in the mapping system for the same
ITR, the Map-Resolver MUST replace the old filter (i.e., the one
already stored in the system) with the new filter (i.e., the one
included in the Map-Subscribe message).
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An ITR can replace an existing filter by a more specific one by
deleting all filters and install the new ones.
A Map-Resolver that is overloaded or configured by means of a
specific policy to redirect requests sent by a set of ITRs to other
Map-Resolvers, the Map-Resolver MUST reply with a Map-Subscribe-Ack
message with the R-bit set and 'Redirect Map-Resolver IP Address'
field set to the redirect Map-Resolver'address. All other bit flags
MUST be returned unset. Moreover, the Expiry Timer MUST be set to 0.
No Filter MUST be included in the message.
If an event matches one of the filters that have been installed by an
ITR, the Map-Resolvers MUST generate the corresponding unsolicited
mapping update message (e.g., Map-Reply, mapping bulk method).
Upon expiry of the validity timer associated with a filter, the Map-
Resolver MUST delete that filter from its mapping subscription
system.
6. Processing a Map-Subscribe-Ack Message
Upon receipt of a Map-Subscribe-Ack message, the ITR MUST check
whether the message matches a Map-Subscribe message it sent to the
same Map-Resolver. If no matching state is found, the message MUST
be silently dropped. If a state is found, in addition to
authentication checks, the ITR MUST proceed as follows:
o If the U-bit is set, it should expect that unsolicited Map-Reply
messages will be received from this Map-Resolver. Appropriate
security mechanisms (e.g., Access Control Lists) SHOULD be
activated to allow the processing of these incoming unsolicited
Map-Reply messages.
o If the B-bit is set, it should expect that (unsolicited) mapping
bulk transfer messages are supported by this Map-Resolver.
Appropriate security mechanisms (e.g., Access Control Lists)
SHOULD be activated to allow the processing of these incoming
unsolicited bulk transfer messages.
o If the R-bit is set and the 'Redirect Map-Resolver IP Address'
field embeds a valid IP address, the ITR MUST update its Map-
Resolver contact information with the new Map-Resolver's IP
address. The ITR MUST use that IP address for subsequent
exchanges. Optionally, if filters were included in the reply sent
by the Map-Resolver, these filters are used for the destination
EID Map-Resolver address selection.
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o If the message includes one or several filters, the ITR MUST check
whether the same set of filters as those included in the Map-
Subscribe request are carried in the Map-Subscribe-Ack message.
Filters that are not returned in the Map-Subscribe-Ack message may
not be valid or have exceeded a limit. The "Result" code
indicates the reason for not installing these filters. In
particular:
* An ITR that receives the result code set to PARTIAL-FILTERS-
INSTALLED-LIMIT MUST NOT try to install new filters unless it
clears all the filters maintained by the Map-Resolver or it
removes some of them.
* An ITR that receives the result code set to PARTIAL-FILTERS-
INSTALLED-BAD MUST NOT resend the same filters that were not
returned in the Map-Subscribe-Ack message, in subsequent Map-
Subscribe requests.
* An ITR that receives the result code set to FILTERS-PROHIBITED
MUST NOT include the filters that were not returned in the Map-
Subscribe-Ack message, in a Map-Subscribe message sent to that
Map-Resolver.
* An ITR that receives the result code set to PARTIAL-FILTERS-
INSTALLED-LOCAL SHOULD wait for at least 60 seconds before
issuing another Map-Subscribe message to install the filters
that were not returned in the Map-Subscribe-Ack message.
o The ITR MUST adjust the Expiry Timer carried in the Map-Subscribe-
Ack. Subscription should be renewed before the expiry of that
timer.
7. Subscription to Multiple Resolvers
In order to subscribe to multiple Map-Resolvers, an ITR sends Map-
Subscribe messages to a list of Map-Resolvers. Each of these
requests is handled as specified in Section 4.
8. Sample Examples
This section includes a set of examples to illustrate the usage of
the methods defined in Section 2.
8.1. Map-Resolver Redirect
The example shown in Figure 3, illustrates an example of an ITR
(ITR1) that is redirected to another Map-Resolver (MR2).
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